The present invention relates to a process for analyzing the wheel speed signals for use with automotive vehicles provided with an anti-locking and/or traction slip control system. In these systems brake pressure and/or engine control signals are generated through logical combination and processing of the wheel speed signals. A circuit configuration for carrying out the process also is provided.
Known anti-locking and traction slip control systems require information on the rotating pattern of the individual wheels. Through logical combination of the individual wheel signals and evaluation according to predetermined criteria, the vehicle speed, the road condition and the frictional coefficient for both driving straight forward or around a bend are derived from the wheel speeds. Normally, a vehicle reference speed is determined from the wheel speeds, which determines the brake pressure modulation during a control operation. Measuring the vehicle reference speed directly, for example, by optical methods requires substantial effort and is less reliable. A precise measurement of the individual wheel speeds is, therefore, of high importance. In some situations, only two wheels, such as the non-driven wheels, are available as an information source for the slip control.
In determining and evaluating the wheel speeds, normally the wheel diameter is assumed to be a constant and identical for all wheels, although substantial differences may occur in practice. Such deviations become manifest, for example, once a spare wheel is mounted, the circumference of which may be smaller by 25 percent than the standard wheel. In unfavorable cases, this results in substantial deviations from an optimum control, resulting, for example in an extended stopping distance.
It is, therefore, an object of the present invention to overcome these and other disadvantages and to provide a process which also in cases of varying wheel sizes permits a precise evaluation of the wheel speed signals.